Just to report back on my most recent experience of testing the HD Star v3 device's compatibility with LibreELEC:
LibreELEC 9.2 + 'DVB drivers for DigitalDevices': No device in TVheadend (see here for log)
LibreELEC 9.2 + 'DVB drivers from the latest kernel': No device in TVheadend (see here for log)
At the moment I've found the most reliable option is using the Montage-3103b.v2 branch from b-rad-NDi's media_tree repository, which is based on Linux version 5.2-rc4. Brad appears to have done a lot of work cleaning up the code required for support of the 3103b device. So far the work seems to have been restricted to supporting the 3103b demodulator itself and any associated Hauppauge devices, hence I needed to write a small patch for the dw2102 driver, to get it to use Brad's updated code when the HD Star v3 USB device is detected. I've posted the patch, and some additional information on the GitHub page for Brad's media_tree branch (see here). I've no idea if the patch meets any particular set of guidelines or standards published for the Linux kernel, and, as far as I am aware, it hasn't been tested by anyone else, but it is currently the most reliable way for me to use the satellite tuner, being more reliable than any of the LibreELEC drivers, or any approach I may have previously described in this thread.